A thermal-type air flowmeter capable of directly measuring a mass flow-rate, serving as an air flowmeter that detects an intake air flow-rate of the internal combustion engines of an automobile, and so forth, is in the mainstream.
A proposal has lately been made to manufacture a sensor element of a thermal-type flowmeter on a semiconductor substrate of silicon (Si), and so forth, by making use of a micro-machine technology. With this sensor element of a semiconductor type, a cavity is formed by removing a part of semiconductor substrate, rectangular in shape, and an exothermic resistor is formed on an electrically insulating film several μm in thickness, formed on the cavity, that is, a thin-film part. Further, a temperature sensor (a temperature sensing resistor) is formed upstream, and downstream, respectively, in the vicinity of the exothermic resistor, and discrimination between down-flow and back-flow is possible according to a temperature differential method whereby a flow rate is detected on the basis of a difference in temperature between upstream and downstream, respectively, of the exothermic resistor. The exothermic resistor is as microscopic as several hundred μm in size, and can be formed in the shape of a thin film, so that the exothermic resistor is small in thermal capacity, thereby enabling faster response, and lower power consumption to be attained.
In Patent Document 1, there is described a mount structure for a sensor element, and drive circuits, in the thermal-type flowmeter having the sensor element of the semiconductor type, formation of the so-called chip-package.
In Patent Document 1, there is disclosed a configuration whereby a sensor chip that detects a flow-rate of a liquid, a lead as an external connection terminal electrically coupled to the sensor chip, and a connection between the sensor chip and the lead are coated, provided with an encapsulation resin integrally disposed so as to enable a flow-rate detection part to be exposed. Further, in FIG. 2 of Patent Document 1, there is shown an example in which a drive chip as well is mounted on a metal lead frame concurrently with the sensor chip.